1. Field of the Invention
The invention relates to a digital radio telephone used in a digital mobile radio communication system such as a land mobile/portable phone system and a PHS (Personal Handyphone System) adopting a digital telephone system for example. The invention particularly relates to a digital radio telephone having a function of storing a mate telephone number (hereinafter, referred to as "incoming telephone number") and a function of calling the stored phone number (hereinafter, referred to as "incoming redialing function").
2. Description of the Prior Art
FIG. 11 shows a system configuration of an analog radio telephone having a conventional incoming redialing function disclosed in a laid-open Japanese patent publication No. 5-14274. This type of conventional telephone receives mate telephone number information of an incoming call together with an analog audio signal via a radio channel using a communication channel in a form of a DTMF (Dual Tone Multi Frequency) signal where a plurality of frequency signals are superposed, and then, stores the telephone number information in a memory.
An operation of the incoming redialing function of the analog radio telephone is explained below. First, a radio signal containing control information received via an antenna 6 using a control channel is demodulated by a radio portion 5 and outputted as a control signal which is an analog signal in a base band. Control information in the demodulated control signal is decoded by a decoder 15 and is processed by a microcomputer 10 to establish the radio communication channel. Then, a radio signal containing the telephone number information received via the antenna 6 using the communication channel is demodulated by the radio portion 5 and outputted as the DTMF signal which is the analog signal in 9 base band. The telephone number information in the demodulated DTMF signal is detected, judged, and decoded by a DTMF receiver 16. Then, the output receiver 16 from the DTMF signal is processed by the microcomputer 10 and stored in a memory 12. On the other hand, in case of calling by redialing, the telephone number information stored in advance in the memory 12 by the microcomputer 10 is read out, encoded by an encoder 17, modulated by the radio portion 5, then, transmitted from the antenna 6 as a radio signal.
Since the incoming redialing function in the conventional analog radio telephone constructed as explained above requires the DTMF receiver for detecting the telephone number information in addition to the construction for operating the telephone function itself, there is a problem that the conventional analog radio telephone construction is complicated. Also, since the conventional analog radio telephone redials using the telephone number information stored only in the memory, it is difficult to provide an incoming redialing function having high-performance or multifunction in consideration of user service.
It is an object of the present invention to provide a digital radio telephone having a high-performance incoming redialing function by maximally using the digital processing ability naturally included in a digital radio telephone.